Kenny - the size difference is so striking because the Motorhead is bigger than a standard Dyson head, and the Turbinehead is smaller than standard!
Before seeing the Motorhead in person, I'd assumed that it was basically a slightly reworked DC18 head. In fact, it's about 2-3 inches bigger than a Dyson upright head! I guess they realised the Motorhead's biggest appeal would be the US market, where houses - and thus, expanses of carpet - are generally bigger, and benefit from a slightly wider head. It's quite heavy, but very nimble and agile because it uses a pivoting roller design, much like the DC18. It glides around obstacles, chair-legs etc with a flick of the wrist!
As Shanon says, the Motorhead is much more effective than the Turbinehead, because the 100w motor means the brush-bar bristles can afford to be a lot stiffer, and really groom down into the carpet pile! The Turbinehead's better than a straight-suction nozzle for pet-hair, but whereas the Motorhead is an adequate replacement for an upright vac, I don't think the Turbinehead is really suited to fully-carpeted homes.
Shanon - I LOVE THIS CLEANER!! I don't regret the purchase at all, although it wasn't cheap. I was wondering whether I'd made a wise decision, investing so much money into a canister, when I'm a 95% upright user - but I find it great for use on carpets. Not entirely happy with the wand design when it comes to dusting, but I have my DC31 for that, anyway! I was really excited to get this, and it's totally surpassed my expectations!
